dragonfly BSD say they have implemented UEFI support, but when I try to create a live USB stick, using dd (linux) or various windows apps, the USB doesn't show up as bootable in my boot menu. I notice that a seperate partition with EFI is not being created. What do I need to do to make a UEFI bootable USB stick from which I can install dragonfly to an internal drive?

DragonFly version 4.6 brings brings more updates to accelerated video for both i915 and radeon users, home-grown support for NVMe controllers, preliminary EFI support, improvements in SMP and networking performance under heavy load, and a full range of binary packages.

freeBSD doesn't appear to support installation to eMMC drive on x86-64
openBSD shuts off my usb hub during boot so that I can't input commands
netBSD doesn't appear to support UEFI in the installer
and neither does dragonFly.

You've had no luck perhaps because you have 'unusual' hardware. Even if you somehow get a base system manually installed with DragonFly or NetBSD booting via UEFI, you don't yet know if all the hardware is supported until you can try to boot the kernel.

FreeBSD actually doesn't have a driver for your eMMC so that's simply a non starter. The same may be the case for DragonFly and NetBSD. A Linux dmesg might aid you in finding out more info about the hardware..

Four months have passed since the OP started this topic and by now the latest DF release has full EFI support. I was able to halfway* netboot the install image on my macbook, and can confirm that the EFI boot code works. At least on my machine.

(*) Halfway, because during boot it dropped me into the kernel debugger. But this has either todo with my netboot setup or perhaps some unsupported part of my macbook. I didn't investigate further, but it wasn't EFI-related.